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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Systematic properties of CO emission from galaxies. I - Luminosity function

A sensitive survey of normal galaxies covering a wide range of luminosities and morphological types is combined with galaxy observations in the literature to provide a sample for statistical study. The global CO emission of these galaxies is extrapolated by modeling the galaxies with an exponential radial profile. The maximum-likelihood distribution functions of CO luminosity and CO/H I flux ratio are similar in behavior. Both have long tails of bright galaxies. However, the typical galaxy has a CO luminosity of about 10 to the 6th Jy km/s Mpc-squared or less and a CO/H I ratio of the order of 10 or less. Averages of the distributions of CO luminosity and CO/H I flux ratio are higher for galaxies of Hubble type Sb-Sbc than for groups of earlier or later types. Quantitative estimates of the possible error sources in the conversion of CO luminosity to molecular mass indicates that the peaking of CO emission at intermediate types is a fairly confident result.

Verter, Frances↗
NASA NTRS1988

Infrared polar brightenings on Jupiter. IV - Spatial properties of methane emission

Different polar 'hot spot' differences are revealed between the northern and southern hemispheres of Jupiter by 7.8-micron observations made with NASA's Mauna Kea IR Telescope Facility. While the northern hot spot is fixed, relative to system III coordinates, at 180 + or - 10 deg longitude and 60 + or - 10 deg latitude, the southern hot spot is fixed with respect to neither the system III longitude and latitude, nor the subpolar point, or even Io's position. Voyager I IRIS data show the north polar hot spot to be more extended in longitude than latitude.

Caldwell, John↗
NASA NTRS1993

Sensor fusion for assured vision in space applications

By using emittance and reflectance radiation models, the effects of angle of observation, polarization, and spectral content are analyzed to characterize the geometrical and physical properties--reflectivity, emissivity, orientation, dielectric properties, and roughness--of a sensed surface. Based on this analysis, the use of microwave, infrared, and optical sensing is investigated to assure the perception of surfaces on a typical lunar outpost. Also, the concept of employing several sensors on a lunar outpost is explored. An approach for efficient hardware implementation of the fused sensor systems is discussed.

Collin, Marie-France↗
NASA NTRS1980

Measurement of dielectric properties and determination of microwave emissivity of polluted waters

The dielectric properties of polluted waters are measured with a reflection-type resonant cavity at 1.43 GHz. Very small water samples in quartz tubes of known volume are placed in the center of the maximum electric field. Measurement of the resonance-frequency variation and a change of the cavity's quality factor are used to determine the dielectric properties. The microwave emissivity of the polluted water is then calculated via the Fresnel equation and applied to data reductions of microwave radiometer measurements.

Blume, H.-J. C.↗
NASA NTRS1992

Three-dimensional structured shocks in AM Herculis-type systems. II - Cyclotron emission from ridge-shaped emission regions

The properties of cyclotron emission from accretion shocks in AM Herculis binaries are studied which result from nonuniform accretion onto linearly extended regions on the surface of the magnetic white dwarf. The resulting ridge-shaped postshock structures yield cyclotron spectra with prominent harmonic features over a wide range of viewing aspects, even for high total accretion rates, in contrast to what has been found previously for axisymmetric accretion shocks.

Wu, Kinwah↗
NASA NTRS2022

FOAM Emissivity Modelling with Foam Properties Tuned by Frequency and Polarization

We model the sea foam emissivity as a part of the work done by an international science team on developing a radiative transfer model of reference quality for the ocean surface emissivity from L band to infrared frequencies. The focus here is on the foam emissivity at frequencies from 1 to 89 GHz. Sensitivity study for different foam properties(foam layer thickness and upper limit of the foam void fraction)guided the effort to tune the model by frequency and polarization. The results show that the differences between simulated and observed brightness temperatures decrease when using tuned foam model.

Magdalena D Anguelova↗
NASA NTRS1991

Emission-line and continuum properties of 92 bright QSOs - Luminosity dependence and differences between radio-selected and optically selected samples

The emission line and continuum properties of new spectra of 92 QSOs are investigated. A detailed deconvolution of the semiforbidden C III 1909 A blend reveals that the secondary feature is almost certainly Al III 1859 A. A study of the Mg II 2800 A emission-line profiles suggests that the broad 'shoulders' often observed are probably intrinsic to the Mg II emission line. It is shown that the QSOs discovered by slitless spectroscopic methods do not differ significantly from those discovered by UV excess surveys. Significant correlations with luminosity are found for W(Mg II), W(semiforbidden C III), I(C III)/I(Mg II), and the continuum ratio fv(1909 A)/fv(2800 A). All of the significant correlations are substantially stronger for a radio-selected subsample compared to a radio-quiet subsample. The C IV and semiforbidden C III emission lines each have a mean blueshift relative to Mg II of 450 km/s while semiforbidden C IV has a mean blueshift relative to semiforbidden C III of 200 km/s.

Steidel, Charles C.↗
DOE OSTI2023

Testing AGN outflow and accretion models with C IV and He II emission line demographics in z ≈ 2 quasars

Using ≈190 000 spectra from the 17th data release of the Sloan Digital Sky Survey (SDSS), we investigate the ultraviolet emission line properties in z ≈ 2 quasars. Specifically, we quantify how the shape of C IV λ1549 and the equivalent width (EW) of He II λ1640 depend on the black hole mass and Eddington ratio inferred from Mg II λ2800. Above L/L Edd ≳ 0.2, there is a strong mass dependence in both C IV blueshift and He II EW. Large C IV blueshifts are observed only in regions with both high mass and high accretion rate. Including X-ray measurements for a subsample of 5000 objects, we interpret our observations in the context of AGN accretion and outflow mechanisms. The observed trends in He II and 2 keV strength are broadly consistent with theoretical qsosed models of AGN spectral energy distributions (SEDs) for low spin black holes, where the ionizing SED depends on the accretion disc temperature and the strength of the soft excess. High spin models are not consistent with observations, suggesting SDSS quasars at z ≈ 2 may in general have low spins. We find a dramatic switch in behaviour at L/L Edd ≲ 0.1: the ultraviolet emission properties show much weaker trends, and no longer agree with qsosed predictions, hinting at changes in the structure of the broad line region. Overall, the observed emission line trends are generally consistent with predictions for radiation line driving where quasar outflows are governed by the SED, which itself results from the accretion flow and hence depends on both the SMBH mass and accretion rate.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2010

Mid-IR Properties of an Unbiased AGN Sample of the Local Universe: Emission-Line Diagnostics - 1

\Ve compare mid-IR emission-lines properties, from high-resolution Spitzer IRS spectra of a statistically-complete hard X-ray (14-195 keV) selected sample of nearby (z < 0.05) AGN detected by the Burst Alert Telescope (BAT) aboard Swift. The luminosity distribution for the mid-infrared emission-lines, [O IV] 25.89 microns, [Ne II] 12.81 microns, [Ne III] 15.56 microns and [Ne V] 14.32 microns, and hard X-ray continuum show no differences between Seyfert 1 and Seyfert 2 populations, although six newly discovered BAT AGNs are shown to be under-luminous in [O IV], most likely the result of dust extinction in the host galaxy. The overall tightness of the mid-infrared correlations and BAT luminosities suggests that the emission lines primarily arise in gas ionized by the AGN. We also compared the mid-IR emission-lines in the BAT AGNs with those from published studies of star-forming galaxies and LINERs. We found that the BAT AGN fall into a distinctive region when comparing the [Ne III]/[Ne II] and the [O IV]/[Ne III] quantities. From this we found that sources that have been previously classified in the mid-infrared/optical as AGN have smaller emission line ratios than those found for the BAT AGNs, suggesting that, in our X-ray selected sample, the AGN represents the main contribution to the observed line emission. Overall, we present a different set of emission line diagnostics to distinguish between AGN and star forming galaxies that can be used as a tool to find new AGN.

Weaver, K. A.↗
NASA NTRS2014

Dust and Gas in the Magellanic Clouds from the Heritage Herschel Key Project. I. Dust Properties and Insights into the Origin of the Submm (Submillimeter) Excess Emission

The dust properties in the Large and Small Magellanic Clouds are studied using the HERITAGE Herschel Key Project photometric data in five bands from 100 to 500 micromillimeters. Three simple models of dust emission were fit to the observations: a single temperature blackbody modified by a powerlaw emissivity (SMBB), a single temperature blackbody modified by a broken power-law emissivity (BEMBB), and two blackbodies with different temperatures, both modified by the same power-law emissivity (TTMBB). Using these models we investigate the origin of the submillimeter excess; defined as the submillimeter (submm) emission above that expected from SMBB models fit to observations < 200 micromillimeters. We find that the BEMBB model produces the lowest fit residuals with pixel-averaged 500 micromillimeters submillimeter excesses of 27% and 43% for the Large and Small Magellanic Clouds, respectively. Adopting gas masses from previous works, the gas-to-dust ratios calculated from our fitting results show that the TTMBB fits require significantly more dust than are available even if all the metals present in the interstellar medium (ISM) were condensed into dust. This indicates that the submillimeter excess is more likely to be due to emissivity variations than a second population of colder dust. We derive integrated dust masses of (7.3 plus or minus 1.7) x 10 (sup 5) and (8.3 plus or minus 2.1) x 10 (sup 4) solar masses for the Large and Small Magellanic Clouds, respectively. We find significant correlations between the submillimeter excess and other dust properties; further work is needed to determine the relative contributions of fitting noise and ISM physics to the correlations.

Magellanic↗
NASA NTRS1989

Characteristics of interplanetary type II radio emission and the relationship to shock and plasma properties

A large sample of type II events is the basis of the present study of the properties of interplanetary type II bursts' radio-emission properties. Type II spectra seem to be composed of fundamental and harmonic components of plasma emission, where the intensity of the fundamental component increases relative to the harmonic as the burst evolves with heliocentric distance; burst average flux density increases as a power of the associated shock's average velocity. Solar wind density structures may have a significant influence on type II bandwidths.

Lengyel-Frey, D.↗
NASA NTRS2010

A Global Modeling Study on Carbonaceous Aerosol Microphysical Characteristics and Radiative Effects

Recently, attention has been drawn towards black carbon aerosols as a short-term climate warming mitigation candidate. However the global and regional impacts of the direct, indirect and semi-direct aerosol effects are highly uncertain, due to the complex nature of aerosol evolution and the way that mixed, aged aerosols interact with clouds and radiation. A detailed aerosol microphysical scheme, MATRIX, embedded within the GISS climate model is used in this study to present a quantitative assessment of the impact of microphysical processes involving black carbon, such as emission size distributions and optical properties on aerosol cloud activation and radiative effects. Our best estimate for net direct and indirect aerosol radiative flux change between 1750 and 2000 is -0.56 W/m2. However, the direct and indirect aerosol effects are quite sensitive to the black and organic carbon size distribution and consequential mixing state. The net radiative flux change can vary between -0.32 to -0.75 W/m2 depending on these carbonaceous particle properties at emission. Taking into account internally mixed black carbon particles let us simulate correct aerosol absorption. Absorption of black carbon aerosols is amplified by sulfate and nitrate coatings and, even more strongly, by organic coatings. Black carbon mitigation scenarios generally showed reduced radiative fluxeswhen sources with a large proportion of black carbon, such as diesel, are reduced; however reducing sources with a larger organic carbon component as well, such as bio-fuels, does not necessarily lead to a reduction in positive radiative flux.

Bauer, S. E.↗
NASA NTRS1988

Electrochromic Variable-Emissivity Surfaces

Temperature controlled by altering infrared radiative properties. Infrared emissivity of electrochromically active layer changed by applying voltage to insert or remove Li atoms electrochemically. Change reversible and continuously variable between specified limits of layered structure.

Rauh, R. David↗
NASA NTRS1998

Emission Lines and the High Energy Continuum

Quasars show many striking relationships between line and continuum radiation whose origins remain a mystery. FeII, [OIII], Hbeta, and HeII emission line properties correlate with high energy continuum properties such as the relative strength of X-ray emission, and X-ray continuum slope. At the same time, the shape of the high energy continuum may vary with luminosity. An important tool for studying global properties of Quasi Stellar Objects (QSOs) is the co-addition of data for samples of QSOS. We use this to show that X-ray bright (XB) QSOs show stronger emission lines in general, but particularly from the narrow line region. The difference in the [OIII]/Hbeta ratio is particularly striking, and even more so when blended FeII emission is properly subtracted. Weaker narrow forbidden lines ([OII] and NeV) are enhanced by factors of 2 to 3 in both UV and optical XB composite spectra. The physical origin of these diverse and interrelated correlations has yet to be determined. Unfortunately, many physically informative trends intrinsic to QSOs may be masked by dispersion in the data due to either low signal-to-noise or variability. An important tool for studying global properties of QSOs is the co-addition of data for samples of QSOS. We use this to show that X-ray bright (XB) QSOs show stronger emission lines in general, but particularly from the narrow line region. The difference in the [OIII]/Hbeta ratio is particularly striking, and even more so when blended Fell emission is properly subtracted. Weaker narrow forbidden lines ([OII] and NeV) are enhanced by factors of 2 to 3 in both UV and optical XB composite spectra. We describe a large-scale effort now underway to probe these effects in large samples, using both data and analysis as homogeneous as possible. Using an HST FOS Atlas of QSO spectra, with primary comparison to ROSAT PSPC spectral constraints, we will model the Big Blue Bump, its relationship to luminosity and QSO type, and we will analyze and contrast line emission and UV/X-ray continuum properties. Absorption of the continuum near the broad emission line region may play a profound role, which we will be able to constrain by direct analysis of observed UV/X-ray spectral absorption.

Green, Paul↗